In general, in treatment of dysfunctions of tempromandibular joint such as tempromandibular arthrosis, bruxism, and malocclusion, there has been used an orthodontic treatment in which an orthodontic appliance having a thickness of 1.about.3 mm and having a shape so as to cover a tooth occlusal surface, called as a splint or a bite plate, is set in the oral cavity of a patient for a certain period of time, thereby leading a mandibule to a normal position.
Usually, in the preparation of such an orthodontic appliance, acrylic resins such as dental self-curing resins or heat-curing resins are used, and these resins are applied in the following procedures.
In case where a self-curing resin is used, while using a gnathostatic model which is prepared by setting a plaster model prepared by impression taking of a dentition of a patient in an articulator, thereby reproducing the oral cavity, a self-curing resin powder is first mixed with a liquid to prepare a paste; the paste is then made in a plate-like state and formed upon light adaptation on the dentition of the gnathostatic model, followed by achieving both occlusal equilibration and adjustment of surface characterization; and after the resin has been cured, adjustment of surface characterization such as one on the marginal shape as well as polishing are achieved.
On the other hand, in case where a heat-curing resin is used, while using a gnathostatic model as prepared in the same manner as in the case of a self-curing resin, a wax model having the same type as in an orthodontic appliance is first prepared on the gnathostatic model by using a wax; the wax model is invested in a flask by using a plaster; after the resin has been cured, voids obtained after removing the wax with hot water, etc. are filled with a resin in a dough stage as prepared by mixing a heat-curing resin powder with a liquid; the resin is cured upon heating for a certain period of time; the cured resin is then excavated out from the flask; and adjustment of surface characterization as well as polishing are achieved.
As described above, since the preparation of the conventional orthodontic appliance is carried out in an indirect method using the gnathostatic model in which the oral cavity is reproduced, such is the present state that not only it takes plenty of time and labor, but also since all of these working steps must be manually carried out, there is often a scattering depending on the technician so that a fully satisfied precision is hardly obtained. Also, since rigid and brittle properties inherent in the acrylic resin are succeeded to the finished orthodontic appliance, the orthodontic appliance is generally poor in elasticity and is likely broken. In addition, although the orthodontic appliance such as a splint is usually retained in the oral cavity by utilizing a tooth undercut, in case where the undercut is designed to be large in order to have a high retention strength, the material poor in elasticity makes the orthodontic appliance readily break at the time of placement and removal. On the other hand, in case where the undercut is designed to be small, there is a drawback that the orthodontic appliance can not be thoroughly retained, whereby it is likely to drop. For these reasons, such problem is caused which requires to retain the orthodontic appliance by newly providing with a clasp, etc., and the structure of the orthodontic appliance becomes inevitably complicated so that the preparation and adjustment of the appliance are extremely difficult, whereby it takes plenty of time and labor.